The international community is trying to complete an agreement banning lethal autonomous weapons—“killer robots”—but the United States and United Kingdom are slowing down the process, possibly by years, according to supporters of the ban.

Officials from those two countries are reportedly “seeking to water down” the agreement, The Guardian reported, so it applies only to emerging technology in the field of military robots, and not any systems that could be deployed before the treaty takes effect.

“The U.K. and U.S. are both insisting that the wording for any mandate about autonomous weapons should discuss only emerging technologies. Ostensibly this is because there is concern that … we will want to ban some of their current defensive weapons like the Phalanx or the Iron Dome,” Noel Sharkey, a professor of artificial intelligence and robotics at the University of Sheffield and co-founder of the International Committee for Robot Arms Control, a coalition of robotics experts who are campaigning against the military use of robots, told The Guardian.

Such a development would undermine the intent of the agreement, and result in autonomous weapons systems becoming a part of modern warfare. “There is a problem with them being able to discriminate between civilian and military targets—there is no software that can do that,” Sharkey said.

“If there is not a pre-emptive ban on the high-level autonomous weapons then once the genie is out of the bottle it will be extremely difficult to get it back in,” Christof Heyns, the U.N. special rapporteur on extrajudicial, summary or arbitrary executions, told The Guardian.

Heyns added: “There is indeed a danger now that [the process] may get stuck.”